Frontal squareness deviation refers to the amount of error in the perpendicular structure of a measurement tool. In other words, frontal squareness deviation relates to the linear axes of motion that a metrology tool is capable of and the amount or deviation from complete perpendicular motion. Knowing the frontal squareness deviation of a measurement device is crucial for getting an accurate and precise measurement readout. Frontal squareness deviation is expressed in the context of the circle of rotation of the instrument. Testing for frontal squareness deviation, perpendicularity of motion, and parallelism are all very important for conducting precise measurements.